Semiconductor memory circuits include, for example, static random access memory (SRAM), dynamic random access memory (DRAM), read only memory (ROM), and other non-volatile memory circuits. While the size of a memory circuit becomes smaller and its capacity becomes larger, variations in manufacturing process have greater impacts to the performance of the memory circuit.
For example, a “weak bit” is a memory cell in a memory circuit where the memory cell has a relatively low current driving capability or a relatively high leakage current compared with a normal bit due to process/device variations. The weak bit results in a slow response time and affects the performance of a memory circuit. For example, the cell current of a weak bit may be 30% lower than a normal bit due to process/device variation, and the operating frequency may also be degraded by more than 30%.